1. Field of the Invention
The present invention relates to a rotation detector designed to prevent line disconnection from being caused by an abrupt thermal change.
2. Description of the Prior Arts
FIG. 1 shows a sectional side elevation view of a conventional rotation detector disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2003-98019.
The conventional rotation detector is used to detect a rotation angle of a shaft. It has a rotary shaft 104a and a rotary shaft 104b arranged in series in a central portion of a cylindrical housing 101. An outer core 110 and a stator core 130 are mounted in parallel outside the rotary shaft 104a but inside the housing 101 while an inner core 120 is mounted on the rotary shaft 104a oppositely to the outer core 110. A rotor core 140 is mounted on the rotary shaft 104a oppositely to the stator core 130.
In the outer core 110, a core 112 is provided surrounding a side face of a bobbin 111 including a coil 113 formed by winding a wire into a form of a winding, the ends of which coil 113 are connected to outer core pins 115a and 115b placed side by side on a connection base 150 in the horizontal direction respectively. The inner core 120 includes a coil 123 formed by winding a wire into a form of a winding.
In the stator core 130, coils 133 are formed by winding wires into a form of a winding on a plurality of annular stator core teeth 131 arranged on an annular base plate 132. Four ends of the coils 133, which are connected to each other in X direction (the horizontal direction) and in Y direction (the vertical direction), are connected through the annular base plate 132 to stator core pins 135a, 135b, 135c and 135d which are placed side by side in the horizontal direction on the annular base plate 132. In the rotor core 140, a coil 143 is formed by winding a wire into a form of a winding on a plurality of annular rotor core teeth 141 arranged on the rotary shaft 104a. 
The connection base 150 is fixed with a fixing bolt 102 outside of the housing 101. The outer core pins 115a and 115b and the stator core pins 135a, 135b, 135c and 135d are attached to the connection base 150, which is surrounded by a cover 103.
The conventional rotation detector has the same configuration for detecting a rotation angle of the rotary shaft 104b as that for the rotary shaft 104a and therefore is capable of detecting a rotation angle for the rotary shaft 104a and the rotary shaft 104b, respectively.
The conventional rotation detector, however, has the following problem.
FIG. 2 illustrates in an enlarged scale a fixing state of the connection base 150 in the conventional rotation detector shown in FIG. 1.
As shown in FIG. 2, the outer core pins 115a and 115b are attached to a bobbin terminal 114 provided in the bobbin 111, and the stator core pins 135a, 135b, 135c and 135d are attached to the annular base plate 132 via a stator core terminal 134. The connection base 150 is, as shown in FIG. 1, fixed to the housing 101 with the fixing bolt 102. The outer core pins 115a and 115b and the stator core pins 135a, 135b, 135c and 135d are inserted into through-holes 152 with conductive coatings 151 formed on the through-holes 152 bored in the connection base 150, respectively, and fixed to the conductive coatings 151 with solder 153.
When there is an abrupt thermal change applied to the conventional rotation detector, any forces as indicated by arrows A and B will be exerted on a portion between the connection base 150 and the outer core pins 115a and 115b or the stator core pins 135a, 135b, 135c and 135d due to a difference in a coefficient of thermal expansion between the housing 101 formed of metal and the bobbin 111 formed mainly of resin material to which the outer core pins 115a and 115b are attached or the annular base plate 132 formed of, for example, glass epoxy resin material to which the stator core pins 135a, 135b, 135c and 135d are attached. For example, for the housing 101 with a diameter of 50 mm, the additional forces may cause a relative shift of 0.1 to 0.2 mm between the connection base 150 and any of those pins. Therefore, there is a possibility of an occurrence of a crack or a breakage on the solder 153 fixing the connection base 150 to the outer core pins 115a and 115b or to the stator core pins 135a, 135b, 135c and 135d, thereby causing line disconnection in the connection base 150.